S. W. McBlRNEYl
One of the questions of major importance in connection with mechanized t h i n n i n g of sugar beets is the effect on yields of single and double plants left by the t h i n n i n g operation. A set of plots was p u t in this past s p r i n g at F o r t Collins in cooperation with the Colorado A & M College to determine in p a r t the answer to this question. Sev- eral others are also working on different phases of the same question and when all the information is brought together we hope to have an answer.
in mechanized t h i n n i n g operations double p l a n t s frequently oc- cur a n d they are usually counted in one of two ways in d e t e r m i n i n g after-thinning stands. Sometimes the double is counted as two beets to give the total n u m b e r of beets per h u n d r e d feet of row. Some- times the double is counted as a hill along with the singles as separate hills to give the total number of hills per h u n d r e d feet. There has been a difference of opinion with mechanical t h i n n i n g as to whether the number of beets or number of hills should be k e p t at the desired thinned stand, for example of 100 per h u n d r e d feet of row.
This m a t t e r of total number of beets versus total number of hills was taken into consideration when the set of plots was laid out. On p a r t of the plots the total n u m b e r of thinned beets was kept at 100 per h u n d r e d feet of row and the percentage of t h e beets which were singles a n d doubles was varied in 20-percent steps from 100 percent singles to zero percent singles and 100 percent doubles. This meant t h a t the n u m b e r of hills for these plots was 100 hills for 100 percent singles, 90 hills for 80 percent singles, 80 hills for 60 percent singles a n d down to 50 hills for 100 percent doubles. On the r e m a i n d e r of the plots the number of t h i n n e d hills was k e p t constant at 100 per h u n d r e d feet and the percentage singles as before was varied by 20- percent steps from 100 percent singles to zero singles a n d 100 percent of the hills as doubles. On this group of plots the n u m b e r of beets was 100 beets for 100 percent singles, 120 beets for 80 percent singles and 20 percent doubles, a n d up to 200 beets for zero singles a n d 100 percent doubles.
The plots were carefully h a n d thinned by 10-foot sections of row so t h a t each section had its desired n u m b e r of single a n d double plants. The p l a n t i n g was with 7 to 1 0 / 6 4 " segmented seed at 4 to 6
1Agricultural Engineer, Bureau of Plant Industry, Soils and Agricultural Enginee- ing, U. S. P. A., Fort Collins, Colo.
P R O C E E D I N G S — F O U R T H G E N E R A L M E E T I N G 175
p o u n d s p e r acre, but germination was good a n d t h e r e were enough dou- bles to obtain the desired stands. Some of the double p l a n t s were r i g h t together when they were thinned, h a v i n g evidently come from a dou- ble-germ segment or two segments d r o p p e d together. O t h e r double p l a n t s were s e p a r a t e d by an inch or two a n d evidently came from two segments. No a t t e m p t was m a d e to t r y to get doubles of one t y p e or the other, but there were p e r h a p s about as m a n y of one as the other. Plots were four rows wide a n d about 35 feet long so t h a t 30 feet of the two center rows could be harvested a n d avoid border effect. E a c h t r e a t m e n t was replicated five times in randomized blocks.
These plots together w i t h t h e rest of t h e field were carried t h r o u g h to harvest, being i r r i g a t e d t h r e e times a n d being cultivated a n d hoed a n d otherwise t r e a t e d all alike. They were harvested in early October.
The plots were harvested by h a n d , keeping the two 30-foot rows in each plot s e p a r a t e . The beets wTere washed to eliminate discrep- ancies of d i r t t a r e . The d a t a t a k e n included number a n d weight of marketable beets, a m a r k e t a b l e beet being taken as one of 11/4 inch or g r e a t e r diameter, a n d t h e t o t a l n u m b e r of beets including u n m a r - ketable roots so as to get a check on losses of numbers of beets from t h i n n i n g to h a r v e s t time.
Table 1 shows the d a t a t a k e n on this set of plots. In general all the beets left at t h i n n i n g time were accounted for at harvest either
T a b l e 1 .
H a r v e s t s t a n d T h i n n e d s t a n d
P e r c e n t - a g e d o u b l e s
0 20 40 60 8O 100 20 40 60 80 100
B e e t s p e r 100 feet
100 100 100 100 100 LOO 120 .140 160 180 200
H i l l s p e r 100 f e e t »
100 90 80 70 60 50 100 100 100 100 100 D i f f e r e n c e f o r s i g n i f i c a n c e
T o t a l b e e t s p e r 100 feet
100.0 100.0 98.6 105.0 95. 6 I01.7 119.0 139.0 147.5 163.2 174.5
b e e t s p e r 100 feet
97.0 94.6 95.5 97.6 92.4 94.0 111.0 122.3 126.3 131.6 137.5
Yield T o n s p e r a c r e
12.25 12.31 12.31 11.66 12.52 11.07 11.75 10.27 9.82 9.21 9.82 + 1.17
P e r c e n t of c h e c k
100 101 101 95 102 90 96 84 80 75 80
as m a r k e t a b l e or unmarketable roots up to the point where t h e t h i n n e d s t a n d was 140 beets per h u n d r e d feet of row. W i t h heavier t h i n n e d s t a n d s p a r t of the beets did not grow t h r o u g h u n t i l h a r v e s t to make roots large enough to find. W h e n the n u m b e r of t h i n n e d
T r e a t m e n t N o .
176 AMERICAN SOCIETY S U G A R - B E E T TECHNOLOGISTS
beets p e r h u n d r e d feet was kept at 100, even though the percentage of doubles increased to 100, nearly all the beets came t h r o u g h to h a r - vest as marketable beets. However, when the n u m b e r of thinned hills was kept at 100 per h u n d r e d feet a n d the number of beets in the thinned stand increased as the percent of doubles increased, the n u m - ber of marketable beets increased steadily but the n u m b e r which did not make marketable beets also increased.
The yield data are shown in the last two columns of the table, one being expressed in tons per acre and the other in percent of the check treatment which was 100 beets per h u n d r e d feet of row, all beets be- ing singles. The differences in yield between t r e a t m e n t s in tons p e r acre required for significance at the 95-percent level is shown. This data shows t h a t when the number of t h i n n e d beets is k e p t at 100 per h u n d r e d feet, the yield is not decreased by increased percentages of doubles until the percentage of doubles exceeds 50 or 60 percent. Be- yond this point there is a downward t r e n d of yield which barely reaches significance with 100 percent doubles. However, when the number of beets left at t h i n n i n g increased as the percentage of dou- bles increased, the yield decreased even though the n u m b e r of hills was kept constant at 100 per h u n d r e d feet. This decrease was sig- nificant with 40 percent or more doubles.
The trends of yields with increased percentages of doubles is shown even better by the curves in F i g u r e 1 t h a n by the t a b u l a t e d data. The curves are estimated from the plotted data. The u p p e r
PERCENT OF DOUBLES IN THINNED STAND
Figure 1.—Curves showing the effect on harvest yield of varying percentages of.
single and double beets.
P R O C E E D I N G S — F O U R T H GENERAL. M E E T I N G 177 curve indicates t h a t w h e n the t h i n n e d s t a n d is k e p t at 100 beets p e r
h u n d r e d feet t h e r e is only a small decrease in yield even with a com- p a r a t i v e l y high p e r c e n t a g e of doubles. On the other h a n d the lower c u r v e indicates t h a t w i t h increased doubles a n d a corresponding in- crease in n u m b e r of t h i n n e d beets p e r h u n d r e d feet t h e r e is a signifi- c a n t decrease in yield which reaches a 25-percent decrease at about 80 p e r c e n t doubles.
It should be pointed out t h a t this set of plots was grown on a field h a v i n g a 12- to 13-ton-per-acre level of soil fertility. The d a t a probably would have been different on soil of a higher or lower fer- tility level. The s t a n d of 100 beets per h u n d r e d feet of row was t a k e n as a check because t h a t seems to be the commonly accepted de- sired t h i n n e d s t a n d in this a r e a .